1. Lecture 8 Electronic Commerce Modelling Techniques

2. This Lecture Review of SDLC Object modelling
Partly worked example of object modelling
References:
Hawryszkiewycz (2001) Systems Analysis and Design, Prentice Hall

3. FEASIBILITY STUDY · establish feasibility & business case
Systems Development Life Cycle (SDLC)
FEASIBILITY STUDY · establish feasibility & business case
· client (sponsor)
· system analyst
SYSTEM ANALYSIS
· determine system requirements
· understand old system and problems
· logical view of the system
· system analyst
· managers
· users
SYSTEM DESIGN
· physical design the system
· system analyst
· developers
IMPLEMENTATION
· install and test · train users
· documentation & user manuals
· system analyst
· developers
· users
POST INSTALLATION & REVIEW · fix errors
· maintain program
· add enhancements
· developers
· users

4. Models in Development Strategic Design SWOT Business Model
System Model
Implementation Model
SWOT
Rich pictures Scenarios
Structured systems analysis Object modelling
Programs & databases

5. Object Orientation and the Linear Cycle
System Analysis
Use case model
Usage world
Use cases and object class diagram of existing system
Requirements Analysis
System world
Object class diagram of new system
System Design
System world
Object languages
System Development
Implementation world
Testing
Use cases
Implementation world

6. Object Modelling Approach
Use Cases
User requirements (Rich pictures) ?
Sequence diagrams
Event flow diagrams
State transition diagrams
Object Classes
System design model

7. Example Using an Automatic Teller Machine
What are the activities that take place through an ATM?
Withdrawing cash
Transferring funds between accounts
Depositing funds
Getting reports e.g. balance

8. Scenarios Rich Pictures
Scenarios illustrate the system dynamics by modelling sequences of actions in the user world
Rich picture diagrams are one way to model interactions
Scenarios may describe:
Processes followed
Problem solutions

9. Rich Picture for ATM Card Withdraw cash Insert card Enter PIN
Remove card
Balance
ATM
Bank
Deposit
Account
Person
Cash
Report Slip

10. Use Case Model A use case model defines all use cases and the actors
Each use case has a script and actors
Actors are active elements
Customers, bank systems
The script describes the set of steps for a specific activity
Alternate steps must be included

11. ATM Use Case Model Withdraw cash Transfer funds Bank System Customer
Deposit funds
Get report
Bank System
Customer
Operator

12. Use case – ATM withdraw cash
A greeting message is waiting on the ATM
The customer inserts card into machine
ATM asks customer for PIN
Customer enters PIN
ATM displays customer’s account and requests selection
Customer selects an account
Machine displays account limits
Customer keys in withdrawal amount
The money is dispensed
Card is ejected
Receipt is printed out

13. An alternative course of events must be written for each exception
Alternatives Events
What if card is not accepted?
What if the customers enters an incorrect PIN?
What if the withdrawal is too large?
What is the customer stops the process and with draws the card?
An alternative course of events must be written for each exception

14. Final Use Case Script ATM Withdraw cash Normal course ……… ……… ………
Alternative courses
………

15. Use case to objects Each use case is examined to identify objects
Three objects can be readily identified in the ATM withdraw cash use case
Customer
ATM
Bank System

16. Objects communicate Object 1 Data + Methods Object 2 Data + Methods
Message
Response

17. Sequence Diagram Describe messages exchanged between objects
Sequence diagram rules
Generally, each actor becomes an object
Time moves downwards
No decisions are shown
Create a sequence diagram for each use case
Every alternative has its own sequence diagram

18. Sequence Diagram Customer ATM Bank System Customer card
Request for PIN
PIN
PIN & card details
PIN OK for account #s
Account numbers
Selected account
Selected account
Limits
Limits
Amount
Amount
Approval
Receipt

19. Transition Diagrams
Models dynamics of the system as the system state changes as a result of messages and events
Circles or ellipses represent state of an object
An arrow represents a change

20. ATM Transition Diagram
Customer inserts card
Receipt
Print receipt dispense cash
Idle
Reading card
Request PIN
Waiting for PIN
Customer enters correct amount
Customer removes card
Enters PIN
Limit exceeded
Waiting for selection
Waiting for selection
Ask bank to check PIN
Request PIN again
Display “Invalid PIN” msg
Limit reminder
Request security check
Limits
Display limits
Waiting for selection
Displaying accounts
Waiting for authority
Customer selects account
Accounts
PIN OK
Source: Hawryszkiewycz (2001) p.287

21. Event Flow Diagram Bring all sequence diagrams together
Get everything to do with an object in one place
Obtain a first cut of the object class
Note:
All objects in the sequence diagrams appear only once in the event flow diagram
All messages are shown in the event flow diagram

22. Event Flow Diagram Event flow diagram Use Case 1 Simple flow Exception
Sequence diagram 1
Sequence diagram 2
Event flow diagram
Use Case 2
Simple flow
Exception
Sequence diagram 3
Sequence diagram 4

23. Simplified Event Flow Diagram
Customer inserts card
PIN and card information
CUSTOMER
get-PINrequest; get-accounts; get-limits; get-receipt;
ATM
get-card; get-PIN; get-account; get-amount; get-PINOK; get-limits; get-approval; CUSTOMER
get-PINrequest; get-accounts; get-limits; get-receipt;
BANK SYSTEM
get-PIN&Card; get-selection; get-amount;
Customer enters PIN
Selected account amt
Selected account amt
PINOK / account numbers
Request PIN Display accounts Display limits Receipt
Limits approval

24. First cut object class Attributes Methods OBJECT1 A B C D E F G
get-msg1(A,B); get-msg2(C,D); get-msg7B,D); get-msg8(A,F);
Msg1(A,B)
Msg2(E,F)
Msg5(A,F)
Msg7(E,G)
OBJECT1
Msg3(A,E)
Msg4(E,F)
Msg7(B,D)
Msg8(A,F)
Attributes
Methods

25. OOSE Development Process
Interfaces Use case model
Concept formation
Requirements Model
Subject noun list Object class model with methods
Requirements definition
Analysis model
Refined object class model with detailed functions, attributes and control
Construction
Design Model
Testing
Implementation level
Objects and methods as programs

26. Object Approach & RAD
Object methods are suitable for prototyping and rapid application development
After JAD start with some objects
connect into the system
Experiment
Add new functionality to objects
Add new objects
Use objects from a library
Specialise them and save (object reuse)

27. Business Process Improvement Modelling Workflows
A way of modelling the business functions
Modified flowcharting
OK for process modelling – used in BPR
Users can understand

28. Private Study
Workshop
Build an EC store front using MyFirstStore